Rotor blade



zsheets-snee't 2 H. H. PLATT ET AL y RoToR BLADE Filed May 13,` 1942 Dec. 17, 17946,

rz Laurezzce Le dim/5 Patented been, 194e invention relates-to .airfoil blades vfor `use in aircraft liitingrotors and more particularly in l aircraft deriving their main supportfrom `rotors which are actuated either by direct power drive or,`

by the action of relative airflowV over them,` other- `wisc designated `generically as rotating-wlngvairl.

craft, ,and in whichthe blades are attached to the rotor hub by `pivots, permitting universalV swinging of the blades.l

` It is well known that rotor blades presentdifiifl cult and exacting problems in design, construe-l tion anddurability. `Thus,.correct" performance requires accurate and enduring location `oifjthe s c chordwise centers of .pressure and ofgravity. l, flfo .this end,`the`airfoil section mustbe maintained to a high degree of conformance with the basic airfoil section and the structural design mustbeN capable of accurate weight control,` Q

The blade` must be capableV f withstanding` the very high centriiugalvforces developed'ilduring the rotation and the outerfsurface must `be capable of `withstandingfthe langeandliuctuating aerodynamic pressures developedby ,tllfliigh,`

velocity of rotation,

Furthermore, to prevent .obiectionableL torsion and iiutter, the blade must be supported approximately inthe center of pressure line andv the chordwise location of the` center of gravityoi.each4 element ofclength of the lifting portionrnust be close to the center ofjpressure line as well.V llo` this end, it is customary to include some fornir of` i, counterweight, usually non-structural, near the.; y

leading edge of the blade due to` the fact that the centerof pressure of a suitable airfoil is` much 1 I nearer the leading than the trailing edge.`y

Above "all, the `above requirements must be achieved while maintaining the total weight` of the blade `Within the very narrow limits prescribed, on the one hand by the general require` ment for lightness inaircrait, and onthe other hand by the maintenance of a suitable angle of equilibrium relative tothe rotor axis whileinf nicht.

The type of construction which has hitherto,` been found most suitable for approaching these requirements is one whereina tubular steel spar is used as the main structural element.` "Tofth'is" spar, wood ribs are attached, at spaced inter# vals, by suitable means such as iianged collars i welded `or pinned to `the spar,` the saidtrilcsbeing formed generally to the airioil section desired.

A formed Wood strip is applied atxthe trailing v edge, while the leadingends of the ribs supporti* a counterweightrod of metal and a leading ledg l Application ilVIayllS,

` cciaimsl I45' s, e e c ffbullrheadstoprovidflocal stiffnesswithout the Novem@ Aly isheldftogethenb ue nailsand an.-

comme; @een .ne fabric @vering dos not i maintain anaccurateiairfoil reaction; `the fabric f and plywood" coverings are so delicate thatgdarns age to them in lhandlingis of frequent occurrence; 1othe covering tlnish is not adequately resistant to"` One objtjof our.. present inventionisgtcu` prof` t vide a rotor blade .capable of quantity` production at lowcost. l Another object I accurate contour throughout its .working length, A

Hiace."v`

VtWin11trete and, Y. t t es appear'more fuuyrrom-the renewing detailed description, `appended Q;claims and accompanyingA drawingsfour 'invention contemplates the use of j a tubular "csparior its main structural member; the prefabricationoia seamlessenvelopemolded,l

material,'SI21T` as" reinforced plastiato a Acontour "havingan exterlorairfoil cross-section; `the in` t "sertion4 or lthe vl'tubulary spar througl'i` the hollow interior je; the prerajbricated envelope; fand the *attachment of the envelope to the tubular spar by suitable means" such as collars and ribs, or "lugs, eldedpinnedor boltedtothe spar and screwedtofthe envelope.

\ Ourfjinvention further contemplates the form- Vfing of the envelope 0with a thicker wall inthe Y the purposes *of'better'weight and strength dis-` tribution. Y c c 1 Our'i'n've 'tion' alsoicontemplates the useof an .envelopeffornied withione or more longitudinal tacheddirect'ly to lugssecured tothe spar.` l

Ouriinvent'ion also includes othernovelieatures 50 l .ci vconstructien'fwhich will appearmore fwully from 1 l the following ldet'zliilod description;`

For purposes of lustrating our vention, we

have shown in theaccojmpanyiiig drawings forms .frthereofiiiv usesince satisfactory n 2,412,903? i s isjjapplied. over `the `whole t f y and fshrunl; onfbyfthe applicati@l0f a numben l of coats of dope` JThis typenf Jconstruction r has been `found inpractice,tohayeseriousshortabrasion` and is habiti'rally impairedjby thelaction y l of rainf dxofpsf,"` haihstones or small solid objects picked up `by the wind; the blade can be` made ,s `,.only bywhandfiabricetlon ymethods" `willen make it necessarilyexpensiife in quantity production. i

j Still anotherobject is to provide arotorblade having aruggedanda ramon-resistantcateraar t er objects, view, as t. s

orfotherwise fabricated, of light, strong, resilient l ,c

` spaced ribs I6, which are Vand reliable results, although it is to be understood that our invention is not limited to the precisearrangernent of the instrumentalities as herein vshown and described. l n Referring to the drawings in'which like referf ence'characters indicate like parts: n Figure 1 representsa .plan'viewof an aircraf y having rotor blades embodying our invention. Figure Zrepresents a fragmentary, top elevational view of one of the rotor blades shown in Figure 1, drawn to' a somewhat enlarged scale,

parts being broken awayl better to reveal the construction thereof.L d s Figure 3 represents a cross-,sectional view generally along the line 3 3 of Figure 2;

Figure 4 represents a fragmentary elevational view similar to that of Figure 2 but showing a modified form ofconstruction.

Figure 5 represents a cross-sectional view along the line 5 5 of Figure 4.

Figures"6 and '7 represent cross-sectional views similar to thatA of Figure 5 but showing alternative forms of blade envelope' with different web ar-V rangements from that voi' Figure 5.

' Figure 8 represents a top elevational view of the tip portion of the rotor blade shown in Figures l and 2, parts being broken away' better to reveal the construction'thereof.

Figure 9 represents across-.sectional view,'on

an enlarged scale, along the lines-9. of Figure 1v illustrating a.A detail of construction of the root end portion of a rotor blade made according to our invention..

' The rotor blade of the presentinvention is of atype which has been found'particularly well suited for use in helicopters and autogiros.

Inone embodiment shown in Figures 1, 2, 3 and 8 we may provide' a rotor blade having uniform chord over most of its outboard portion I0, a vtapered tip II and a non-lifting faired tube inboard portion I2. A fairing block I3 provides a smooth transition from the outboard'portion l0 to the inboard portion I2. A retaining collarIII is` formed on, or otherwise attached to the vinboarcl end of the spar I5 for cooperation' with a suitable tting (not shown) on the rotor hub 34.

A central tubular spar I5 forms the structural backbone of the blade and extends throughout most of its length. Within the outboard, working portiony I0, the spar I5 is fitted with suitably v otherwise. f v

The airfoil envelope 'I8 is of molded seamlessy form and may be"prefabricated from any suitplastic.r Its exterior form is molded to the predetermined airfoil contour selected for advantageous performance of the aircraft, or to a form i which may readily` be deformed to such contour whenplaced over the rib and tube skeleton. A counterweight rod 20, of suitably heavy materialL and ofweight sufficientto provide the desired operative balance of the blade, is inserted in the envelope I8 adjacent the leading edge and secured Ain position by means of countersunk head screws 2i, or in any other suitable manner.'v The envelope I8 is slipped into' place over the ribs I6 supported on the spar d d 4 d and then securely attached able means such as cement and nailsjpr drive screws; the nails or screws preferably being countersunk so as to eliminate' surface irregularities.

One method of finishing the tip, which has been found by us to be advantageous, in practice, `is

'illustrated in Figure 8. An extension piece 22 .of smaller diameterl is fitted into the end of the tubular spar I5 and held in vplace by bolts 23, or by other suitable attachment means. The

extension 22 is tapered throughout its length and i has, attached to it, ribs 244 similar to the main ribs I6 but of sizeand form modified to suit the desired tip contour. The counterweight rod 20 may be extended into the. tip as shown, its end being suitably reduced in dimension. n

A ytip block 25, preferably of the same material ask the ribsfis preferably preformed to the de.- signed aerodynamic contour and is integrally formed, or fitted, with the inwardly extending trailing edge reinforcement' 26 of the tapered tip II; In attaching the tip block 25, the envelope I8 is cut open `at the trailing edge and suitably" cut back over the length required forthe tapering tip.V The end of the extension 22 is4 preferablyl fitted into a. locating recess vin the bloei; 25 to which it may be secured by a pin 2l,.- v

and the envelope skin is then tightly pressed down over the tip skeleton and flnallyattached thereto by means similar to the bonding of the envelope I8 to the main ribs I6. The open trailing edges are similarly pressed down onto and attached to the` trailing edge reinforcement piece 26. The

.edges of the envelope skin are the/nl smoothed oil to form a true trailing edge and joint with the tip block-25. n We have found it prefer ble to mold the envela smooth surface ope I3 with a thicker,` w ll adjacent the leading edge than adjacent the trailing edge, as showny particularlyin Figure 3, inv orderto withstand the higher pressures vand lthe greater abrasive action encountered near the'leading edge.. The

wall thickness may, however, be'uniform,y or of any 'other thickness distribution, if out `departing `from our invention.

InvFlgures 4 and' 5, an alternative embodiment desired, withlof the present invention is illustrated. In rthis embodimentthe ribs I6 are omitted and the requisite stiffness is furnished by webs 28 and-29.

preferably molded integrally with an outer envelope 30. The attachment of the envelope 3l) to the sparV I5' may be `achieved bymeans of the boltedfon lugs 3I to which the envelope 30 is ded tachably secured by drive screws 32, the forward web 28 acting as a location guide in assembly."

The counterweight strip 20 is attached as in the embodiment illustrated in Figures 2 and 3.

The tipmay be formed as hereinabove described, s --webs 28and 29 being cut away to permit compression of the skin of the tip portion. f

n j y In Figures 6 and? there are` illustrated alter-A able resihent material such as fabric-reinforced native forms of prefabricated envelopes, that of Figures 6 having only one web and requiring auxiliary locatingmeans for assembling on the spar, andthat of Figure 7 having three Webs for greater rigidity if desired. In ,Figure 9 there is illustrated a form of fairing for the spar I5 over the inboard, inoperative portion of the blade. 'Ihe fairing 33, of-light, nonstructural material, may be attached to the spar by adhesive tape or otherwise. Y

While we have shown the various features of our invention in certain specic embodiments, we

are aware that our invention may be embodied in .to them by any suitother forms without departing from the spirit or essential attributes thereof. Thus, for example, while we have shown our invention as applied to a non-tapering, untwisted blade having its working airfoil applied only to the outboard portion, our invention is equally applicable to blades having full-length 'working surfaces, or having tapered plan form, or having tapered thickness, or having any desired twist, or having any combination of these characteristics. Furthermore, the speciiic methods of attachment of the various parts are susceptible of very Wide variation, both as to type and dimension, without departing from the scope of our invention. We therefore desire the present embodiments to be considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the foregoing description, to indicate the scope of our invention.

The invention having been hereinabove de-y scribed, what is hereby claimed as new and `de sired to be protected by Letters Patent is:

1. In a rotating-wing aircraft having a lifting rotor, a rotor blade comprising a prefabricated form-retaining generally seamless elongated envelope of molded plastic having an external airfoil contour and having an outer longitudinally tapered tip, said tip being reinforced at its trailing edge and terminating in a formed tip-block, the wall of said envelope being thicker at the leading edge than atV the trailing edge thereof, a spar having its inner end operatively attached to the hub of said rotor and having its outer end extending within said envelope along the untapere'd portion thereof, the exposed portion of said spar being faired, a tapered coaxial member extending from said spar and into the tapered tip of said envelope and having its outermost end fastened to said tip-block, and means for attachingsaid envelope to said spar and to said tapered member at a plurality of spaced points.

2. In a rotating-wing aircraft having a lifting lrotor, a rotor blade comprising a prefabricated form-retaining generally seamless elongated en velope of molded plastic or the like having an ex having its outermost end fastened to said tipblock, and means for attaching said envelope to said spar and to said tapered member at a plul rality of spaced points.

3, In a rotating-wing aircraft having a. lifting rotor, a rotor blade comprising a generally seamless form-retaining elongated envelope with external contour of airfoil section, said envelope `having a straight `leading edge and having its trailing edge swept forward at its outer end, a formed tip-block closing the outer end of said envelope, said tip-block having a portion extending along and reinforcingthe swept-forward portion of the trailing edge of said envelope, and

' an inner supporting spar operatively connecting said envelope to the hub of the rotor.

HAVILAND H. PLATI. WYNN LAURENCE LE PAGE. 

